The piezoelectric component is for example a piezoelectric actuator (piezo actuator) having a monolithic actuator body made of a plurality of piezo elements stacked one on top of the other. A piezo element consists of an electrode layer, at least one further electrode layer and at least one piezoceramic layer disposed between the electrode layers. The piezoceramic layer and the electrode layers of the piezo element are interconnected in such a way that an electric field is coupled into the piezoceramic layer by means of an electrical activation of the electrode layers. The coupled-in electric field causes the piezoceramic layer to deflect and consequently results in the deflection of the piezo element.
A described piezoelectric actuator is known for example from DE 100 26 635 A1. In the piezoelectric actuator the piezo elements are arranged one on top of the other in a stacking direction to form a monolithic actuator body. In this arrangement a plurality of electrode layers, which are referred to as internal electrodes, and a plurality of piezoceramic layers are stacked alternately one on top of the other and sintered collectively to form the monolithic actuator body. The piezoceramic layers consist of a lead zirconate titanate (Pb(Ti,Zr)O3, PZT). The electrode layers consist of a silver-palladium alloy. For electrical contacting of the electrode layers, adjacent electrode layers in the stacking direction are brought to two lateral surface sections of the actuator body that are electrically insulated from each other. At each of these surface sections, the actuator body has a strip-shaped metallization.
In the area of the described surface sections of the actuator body, each of the piezo elements is piezoelectrically inactive. As a result of the alternating conducting of the electrode layers to the surface sections, an electric field is coupled into a piezoelectrically inactive area of the piezoelectric layer, the electric field differing markedly from the electric field which is coupled into a piezoelectrically active area of the piezoceramic layer. In contrast to the piezoelectrically inactive area, the piezoelectrically active area of the piezoceramic layer is located directly between the electrode layers of the piezo element.
During the electrical activation of the electrode layers, that is to say during the polarization of the piezoceramic and/or during operation of the piezo actuator, different deflections of the piezoceramic layer occur in the piezoelectrically active area and in the piezoelectrically inactive area due to the different electric fields. As a result thereof, mechanical stresses occur in the piezo element which can lead to what is referred to as a polarity crack transversely to the stacking direction or to the growth of an already existing crack. In this case the polarity crack can continue into the metallization applied to the respective surface section of the actuator body. This leads to an interruption of the electrical contacting of at least a part of the electrode layers of the actuator body.
To ensure that an existing polarity crack in the actuator body does not lead to a failure of the piezo actuator, in the case of the known piezo actuator a flexible electrical connecting element is attached in each case to the laterally applied metallizations of the actuator body. Each of the flexible connecting elements has a plurality of electrically conductive wires. Along the stacking direction of the actuator body the wires of a connector element are soldered onto one of the metallizations. The wires serve for the electrical contacting of the electrode layers of the actuator body (indirectly over the respective metallization). A rigid electrical connecting pin aligned along the stacking direction of the actuator body and to which the wires are soldered is provided for the electrical contacting of the wires of the connecting element. The contacting of the wires and the internal electrodes of the actuator body is ensured even when the deflection of the actuator body (expansion and contraction along the stacking direction) results in a polarity crack transversely to the stacking direction or, as the case may be, to the growth of an existing polarity crack transversely to the stacking direction.
However, a deflection of an existing polarity crack may occur during dynamic operation of the described piezoelectric actuator. The polarity crack grows in an uncontrolled manner. For example, the polarity crack grows parallel to or approximately parallel to the stacking direction rather than transversely to the stacking direction. Longitudinal cracks form in the actuator body. The uncontrolled growth of a polarity crack may be due to unfavorable intrinsic and/or extrinsic influencing variables. Intrinsic influencing variables relate, for example, to a structure of a piezoceramic layer and/or an electrode layer. The structure can lead to an anisotropic crack resistance within the respective layer. The crack resistance is different in different directions within the layer. Extrinsic influencing variables are based, for example, on an electrical leading edge during dynamic operation or on an inadequate clamping of the actuator body.
The uncontrolled growth of a polarity crack can result in the failure of the piezoelectric actuator. The reliability of the actuator is not guaranteed.